Navigational protractor



ug- 6 i940- J. E. LAwToN 2,210,814

NAVIGATIONAL PROTRACTOR Filed Nov. 16, 1939 5 Sheets-Sheet 2 Z ihn,

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- serves the same purpose f printed rose on the ris not available, and

; trated in the accompanying Patented Aug. 6, 1940 uNirED STATES PATENT OFFICE Joseph Edwin Lawton, Application November 16,

(ci. ca -'94) 6 Claims.

Myinvention relates to new and useful imstruments for use in the navigation or piloting of vessels, motor boats, or sailing craft, and in aerial navigation as in surface navigation.

The principal object of the invention resides in the provision of a device of the character described which is relatively simple and inexpensive'in construction, sturdy and easy of adjustment, and when placed in position for use will not easily slip or otherwise produce inaccuracies in reading.

Another object of the invention consists in the provision of a navigational protractor or instrument which will give aA direct reading of magnetic courses and at the same time, a reading of` true courses, if desired.

A still further object of the invention resides in the provision of a device of the character described having a compass rose extremely easy to read because the rose disc, wheny the device is placed in position for use, reads in the same relative position to the directions on the chart as the chart without regard to the course angle being measured. The device may be used on uneven surfaces when a chart table may be used satisfactorily under a very dim light.

With the above and other objects `in view, as the description proceeds, the novel detailsr ofi arrangement of parts, defollowing specification and illusdrawings, and while I have illustrated and described the 'preferred embodiments of the invention, they now-appear to me, it will be understood that such changes may be made as will fall within the scope of the appended claims.

In the drawings: y 1 Fig. 1 1s a plan showing my improved form of instrument or protractor in a position 'on a chart for charting a course. '4

Fig. 2 is a fragmental enlarged plan-showinga portion of the base, the compass rose, 'and T-square, the head of the T-square being parallelwith an edge of the base. Y

Fig. 3 is a view similar to Fig. 2, parts broken away, showing the base swung relative tothe compass rose in charting a course.

Fig. 4 is a. fragmental plan of the base with a portion of the compass rose removed to show the recess for the T-square bar.

Fig. 5 is an end view.

construction, scribed in the Washington, D. G. 1939, serialN. 304,825

Fig. 6 is a section on the line 6--6 of Fig. 2.

v'l is Aa section at right shown in Fig. 6 on the line 1-1 of Fig. Fig 8 isa sectionaldetail showing separated positions before assembly. My improved form of protractor or instrument is used in connection with charts or maps and at afsi'ngle reading it will give the true and magnetic course angle expressed in eitherl degrees or points for any direction between known places orpositions. It can be used with equal facility toplota line of position on a chart from one bearing of -a known fixed object or a fix from two or vmore known fixed objects, whether they be objects' visible by day, navigational lights or aids visible byy night, or radio bearings. The instrument is provided with a means of readily and easily setting the angle of variation for anyl geographical position where being used. To determine a.A course angle it is then necessary only* to place one long edge on the proposed course, draw thestraight edge of the T-square headto alignment `with a meridian and 'read directly from the compass rose disc either the true direction as indicated on the central line on' the base, orv the magnetic direction single line onthe transparent disc over the compass rose disc.- For plotting a line of position or a position rby `bearings it is necessary only -to` intersect theobject observed as marked on the chart 'with `one edge or one corner of the baseA and with the straight edge of the T-square head. alignedwith `a meridian, give the base card a circular or rotary movement until the observedv direction or bearing falls exactly under the lineI on the magnetic indicator disc. If the observedl bearing was 'first reduced to a true ldirection the plotting would .be done in the same manner exceptl that thebearing reading on the ,compass rose discwould be aligned with the central line on the base card.

' With the'above general description of my in*- strument and: manner of use I will now give af detailedV description of the construction thereof. .My prgotractor includes a rectangular ybase sheet l, formed of transparent Celluloid or similar flexible transparent material, having a line 2 through its longitudinal axis parallel with the longsides 3 and 4 and equi-distant from each side. Centered on the axis line, and centrally in :the rectangular base sheet, is securedv a threadedpost' 5, this post having a base 6 which is secured to the base sheet I and -plate 6' by` means ofrivets I or other suitable fastenings.

2; and

parts in The post'5 is enlarged, as shown at 8, to provide a- 55.?

l Y V Y angles tothat as indicated by the the ,post 5itwi1lfpress the magnetic direction intrated a bearing Washer for a purpose and use which will be later brought out.

The compass rose disc is of a diameter slightly less than the Width of the base plate I and has a with 0 at north, 90 at east, 180 at south and 270 at West, reading clockwise and the inner cirtion showing the cardinal, interv-cardinal, intermediate points and by-points, each point being divided also into quarter .Y points. lThis inner compass circle is imprinted so that north of 0 fall on the saine radial line, east and 90, south and 1802 and Westand 270 corresponding like- The Aface Car-d II is secured to the under disc I2, of a-diametersimilar to the face card II,

thel under disc I 2 being of molded plastic or builtdisc; vmaybe provided of correct s1ze to neatly t the enlarged part 8 of the base'sheet post 5.

.A vmagnetic direc-tion ind1cator disc of transdicator disc I9 yagainst the upper surface of the enlargement@ and rmly lock the magnetic in- The arm or blade I4 of the l"square is of transparent Celluloid or similar material and in length is indicated at 23 and the points being charted are `shown at 24 and 25.

Having fully described the detailed constructionI will now 'endeavor to more in detailv set forth the manner in which the instrument is used.

pass rose on charts or otherwise indicated. 'Ihis is done by bringing the head I5 of the T'square against one side edge 4 of` the 'base sheet, thus bringing the zero degree on the compass rose disc in line with thecentral'line 2 of the base 'I he nut '9 is then loosened vso that the magnetic course indicator disc19`may turn freely, and' for westerly variation bringing the line 20 is shown innig. 2).` variation, the line on the disc I 9 will be moved to the `left or Vanti-clockvvise'of 0 on the compass 2 of thefbase-'Sheet I. the line 20, offthe'magnetic disc I9 is in alignment with 40 on the compass rose disc indicating the magnetic coursey by which the Vessel should' be steered. Foru 'plotting'` observed bearings, either edge on the base sheet' I I"isplaced inconmagnetic indicator disc or the true 'indicator line on the base sheet, dependent upon whetherv the observed compass bearing was reduced to a magnetic direction or a true direction respectively. A line drawn on the chart against the edge of the base sheet will thus indicate a line of position. By using the suitable end of the direction indicator line, reversing an observed bearing is not necessary. Plotting radio beacon directions is accomplished in the same manner by placing the edge of the base sheet on the charted position of the source of radio waves. Plotting cross bearings, Ibow and beam bearings, or any other bearings are accomplished in the same manner From the above it will be noted that I have provided a protractor or instrument of relatively simple construction by the use of which course angles may be easily and quickly obtained from any navigational chart for the piloting of a vessel or plane from a point o departure to a point of arrival. Further I wish to lay particular stress on the fact that the compass rose disc is always in the same relative position to the cardinal points on the chart and in use always remains in the same relative position thereby making the reading easy and rapid.

Having fully described my invention what I claim as new and desire to secure by Letters Patent is:

1. An instrument of the character described including a rectangular base sheet having a line through its long axis parallel with the side edges of the base sheet and equi-distant from each edge, a compass rose disc rotatably mounted on the base sheet and having graduations on a face thereof, the line through the longitudinal axis of the base sheet leading to the edge of the cornpass rose disc whereby the position of the line may be read with the graduations on the face of the compass rose disc, a magnetic direction indicator disc rotatably mounted on the base sheet and rotatable relative to the compass rose disc and base sheet and having a line bisecting the same, and means for holding the magnetic direction indicator disc in xed relation to the base sheet while permitting rotation of the compass rose disc relative thereto 2. An instrument of the character described including a rectangular base sheet having a line through its long axis parallel with the side edges oi the base sheet and equi-distant from each edge, a compass rose disc rotatably mounted on the base sheet and having graduations on a face thereof, the line through the longitudinal axis of the base sheet leading to the edge o the compass rose disc whereby the position of the line may be read with the graduations on the face of the compass rose disc, a magnetic direction indicator disc rotatably mounted on the'base sheet and rotatable relative to the compass rose disc and base sheet and having a line bisecting the same, means for holding the magnetic direction indicator disc in fixed relation to the blase sheet while permitting rotation oi' the compass rose disc relative thereto, and a T-s'quare carried by and slidably mounted relative to the compass rose disc.

3. An instrument of the character described position of the line may be read with the graduathe face of the compass rose disc, a magnetic direction indicator disc supported on the enlarged shoulder portion of the post and rotatable relative to the compass rose disc and base sheet and having a line bisecting the same, and means for clamping the compass rose disc in tight 40 engagement with the surface of the enlarged shoulder portion of the post to hold the magnetic direction indicator disc in fixed relation to the et while permitting rotation of the compass rose 'disc relative thereto. 45 5. An instrument of the character described adapted to be used with a navigational chart, including a rectangular base sheet having a line through its long axis parallel with the side edges of the base sheet and equi-distant from each 50 edge, said base sheet being adapted to have an edge portion or its center line intersecting a point of departure and a point oi' arrival on the chart, a compass rose disc rotatably mounted on the base sheet and having .graduations on a face 55 thereof, the line through the longitudinal axis of the base sheet leading to the edge of the compass rose disc whereby the position of the line may be read with the graduations on the face of the compass rose disc, a magnetic direction in- 60 dicator disc rotatably mounted on the base sheet and rotatable relative to the compass rose disc and base sheet and having a line bisecting the same, means for holding the magnetic direction indicator disc in fixed relation to the base sheet 65 while permitting rotation of the compass rose l vdisc relative thereto, and a member carried by the compass rose disc and having a portion adapted to be" aligned with a meridian line on the chart or an edge of the chart. 70 6. An instrument of the character described adapted to be used with a navigational chart, including a rectangular base sheet having a line through its long axis parallel with the side edges of the base sheet and equi-distant from each 75 lincluding a rectangular base 4sheet :having a 4line hrough -itslongfaxis parallel with the side edges base sheet and equi-distant 'from reach edge, a compass rose disc having a recess formed in one face and rotatably mountedon thebase sheet, the compass rose disc having graduations on a Vface thereof, the line through the llongitudinalaxis of the base sheet leading to the edge of the compass rose disc whereby the position of the line may be read with the graduations on TM) the face of the compass rose disc,aA :magnetic direction indicator disc rotatably mounted on the base sheet and rotatable relative to the compass rose disc and base sheet and having a line bisecting the same, means for holding the lmagnetic 15 direction indicator disc in fixed relation to the base sheet while permitting rotation of the compass rose disc relative thereto, and a T-square having a portion slidably mounted in the recess 'n the face of the compass rose disc. 20 An` instrument of the character described including a rectangular base sheet having a line through its long axis parallel with the sideedges of the base sheet and equi-distant from each edge, a post projecting upwardly from the base 25 sheet and provided with an enlarged shoulder a compass rose disc having an opening to receive the enlarged shoulder portion oi the post, the compass rose disc being rotatable relative to the post and base sheet and having 30 graduations on a face thereof, the line through the longitudinal axis of the base sheet leading to the edge of the compass rose disc whereby the be read with the graduations on the face of the meridian line on the chart or an edge of the 10 compass rose disc, a magnetic direction indicator chart.

disc rotatably mounted on the base sheet and JOSEPH EDWIN LAWTON. 

